A traditional technology for voice transmission has been circuit switching. Circuit switching requires a physical connection between the source and destination. If the source and destination cannot be connected, a busy signal is sent to the source and the call must be completed later.
In contrast, packet switching allows digital data to be transmitted even when the source and destination cannot be directly connected. Packet switching also typically results in decreased system cost and increased system reliability. As a result, the use of high-speed packet switching networks to transmit digital data by private corporations has expanded rapidly in the past several years.
The use of two different technologies for the transmission of voice and digital data creates unnecessary redundancy and expense in telecommunication networks. The desire to reduce redundancy and expense associated with telecommunication networks provided impetus for the development of telecommunication network systems capable of integrating data, voice, image and video over high speed digital trunks. These networks use a packet switching technique called cell relay, which is also referred to as asynchronous transfer mode. U.S. patent application Ser. No. 07/285,041 entitled "Packet Voice/Data Communication System for Voice, Data and Deterministic Information," filed Dec. 15, 1988, assigned to the same assignee as the present patent application, and now abandoned, describes a prior integrated packet exchanger ("IPX") that integrates voice and data transmission over T1 lines.
A typically fully-integrated voice and data T1 network includes a number of geographically distant, interconnected nodes, each of which is a packet. exchanger. Associated with each node is a variety of communication equipment. Each node takes existing voice and data streams from its associated communication equipment, assemblies the streams into a more efficient cell format, and then transmits the cells between nodes via cell T1 lines.
A typical prior node handles four classes of cell traffic. Each class of traffic may carry a variety of data formats. Consequently, each class has different characteristics and different service requirements. For example, voice traffic is relatively delay sensitive and loss insensitive. In contrast, data traffic is relatively delay insensitive and loss sensitive, though this also varies with the particular data format. For example, file transfers are less delay sensitive than terminal to host protocols which are typically user interactive. To account for these differences, each class of traffic is placed in a queue, given a different priority, and serviced substantially according to that priority. During congested periods, when network traffic exceeds the network's throughput capabilities, servicing algorithms may discriminate between the traffic according to class.
One disadvantage of one prior queuing and servicing circuitry and method of U.S. patent application Ser. No. 07/285,041 is its bias against cell traffic that must travel through many nodes to reach its destination. U.S. patent application Ser. No. 07/285,041 addresses this bias using timestamps. However, timestamps cannot be practically extended to high-speed traffic due to the timestamp resolution.
Another disadvantage of prior queuing and servicing scheme implemented in U.S. patent application Ser. No. 07/285,041 is the failure to fairly allocate bandwidth among various classes of cell traffic.
Others have attempted to fairly allocate bandwidth in telecommunication nodes. For example, Manolis Katevenis describes a fair queuing method in "Fast Switching and Fair Control of Congested Flow in Broadband Networks," Vol. SAC-5, No. 8, I.E.E.E. J. on Selected Areas in Communications, 1315 (Oct. 1987) ("Katevenis"). Katevenis proposes implementing fair queuing using a queue for each source-destination pair.
A disadvantage of allocating bandwidth according to source-destination pair is that the number of required queues grows as the square of the number of sources.
A disadvantage of Katevenis and U.S. patent application Ser. No. 07/285,041 is that both fail to segregate multicast traffic from non-multicast traffic. The failure to do so can render a telecommunication network unusable during periods of excessive broadcast traffic, commonly referred to as broadcast storms.